Walls or wall systems that constitute buildings are generally produced by superimposing or arranging side by side blocks of stone or brick or other materials, with the interposition of a binder based on lime or cement or other binding materials, without the presence of voids or cavities.
Usually design sizing of such buildings is carried out in fact by considering the entire cross-section of the wall system as reactive, i.e., it is assumed that all of the cross-section of the masonry is involved in the support of the overlying loads; in other words, the presence of voids or cavities inside the wall system is excluded. In terms of strength, the design takes into account an allowable tension for the masonry that is determined by the contribution provided by the strength of the block of brick or stone or other material and by the contribution provided by the strength of the binder used, also by means of laboratory tests.
Once the building has been completed, as time goes by, the bed of binder that is interposed between the blocks or part of the blocks themselves can be disaggregated by the surrounding action produced by water or air or other agents, or can be conveyed elsewhere by filtering streams or can be altered by the chemical action induced by various phenomena, including atmospheric ones.
This reduction of material within the wall cross-section causes the presence of voids of various sizes, with a consequent net reduction of the effective resisting cross-section, a reduction in the allowable tension or an increase in permeability and other effects.
In some cases, this reduction in strength can cause the collapse of the building.
In other cases, entirely intact wall systems which however contain voids might no longer perform their function correctly because they are subjected to boundary or limit conditions that were not planned for during design, such as for example the generation of tensions affecting the wall system with a different intensity or direction with respect to the design, or the presence of fluid adjacent to the walls of the wall systems, with consequent filtering motions between the blocks, or the need for greater thermal insulation on the part of the wall system, or the need to improve the cohesion of the wall structure, or other conditions.
Various systems are known for ensuring in any case the securing of the masonry and its regeneration. These are generally systems that tend to rebuild the wall body by means of so-called “stitch and unstitch” operations, i.e., delicate operations that consist in partial removals of deteriorated bodies, combined with temporary supports of the complementary masonry with auxiliary structures such as props, boards, ties, or others and the complete replacement of the removed parts. This method, in addition to being highly invasive, requires very long execution times and very high costs.
Other wall consolidation systems are known which consist in “choking”, or “hooping”, or the like, the deteriorated masonry. These systems provide for the aid of auxiliary elements to ensure the recovery of the strength of the wall body, such as for example props, ribs, bars or others. These methods, in addition to being highly invasive, modify the original structure and geometry of the wall body, introducing new metallic elements or others that remain visible to the observer. The costs for the application of these methods are generally very high.
Moreover, other systems are known which provide for the injection, horizontally or in any case at right angles to the two larger opposite faces, in the wall system, of cement or chemical mixtures, possibly with additives, in order to fill the voids that have formed. The injections performed horizontally and at right angles to the surface of the wall, in order to ensure that all the voids are reached, must be very numerous, also for the reasons that will become better apparent hereinafter, and therefore the procedure becomes long and onerous. Moreover, the mixtures used, which generally do not expand or have extremely low degrees of expansion, are injected at low pressure by using electric pumps or other devices or by gravity, most of all to avoid the risk of damaging the walls irreversibly. In the methods described above, therefore, a non-expanding or low-expanding material is used which, again to avoid damaging the wall system irreversibly, has a negligible expansion force (which may even not be known) that is most of all uncontrolled and impossible to dissipate.
For all of these reasons, with these methods it is very difficult to ensure both the filling of the all the voids, including the ones located furthest from the injection point, and the complete filling of vertically extended cavities. Finally, indeed because of the cited characteristics, these methods are unable to induce in the masonry a state of tension whereby the mechanical characteristics of the wall system are improved considerably with respect to the situation prior to the intervention.